Abstract: For the high reliability of digital sun sensor in aerospace applications, the SEU-tolerant design for Leon3-based digital sun sensor SoC in RTL level was fulfilled. In considerations of the speed and size of the entire system, we adopt various strengthening methods for different parts of SoC, including triple modular redundancy, EDAC (Error Detection And Correction) circuit, pipeline restart of CPU, forcing cache to miss, etc. in order to evaluate the strengthening effect of registers, we need the soft error sensitivity getting from the fault injection test on the system with register file strengthened. Then, the prototype was implemented in FPGA and compared the speed and overhead with non-strengthened design.